splitxyzgmt - Online in the Cloud

PROGRAM:

NAME

splitxyz - Split xyz[dh] data tables into individual segments

SYNOPSIS

splitxyz [ table ] [ azimuth/tolerance ] [ course_change] [ minimum_distance ] [
xy_filter/z_filter ] [ template ] [ flags ] [ ] [ [level] ] [ -b<binary> ] [ -d<nodata> ]
[ -f<flags> ] [ -g<gaps> ] [ -h<headers> ] [ -i<flags> ] [ -:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

splitxyz reads a series of (x,y[,z]) records [or optionally (x,y,z,d,h); see -S option]
from standard input [or xyz[dh]file] and splits this into separate lists of (x,y[,z])
series, such that each series has a nearly constant azimuth through the x,y plane. There
are options to choose only those series which have a certain orientation, to set a minimum
length for series, and to high- or low-pass filter the z values and/or the x,y values.
splitxyz is a useful filter between data extraction and pswiggle plotting, and can also be
used to divide a large x,y[,z] dataset into segments.

REQUIRED ARGUMENTS

none.

OPTIONAL ARGUMENTS

table One or more ASCII [or binary, see -bi] files with 2, 3, or 5 columns holding
(x,y,[z[,d,h]]) data values. To use (x,y,z,d,h) input, sorted so that d is
non-decreasing, specify the -S option; default expects (x,y,z) only. If no files
are specified, splitxyz will read from standard input.

-Aazimuth/tolerance
Write out only those segments which are within +/- tolerance degrees of azimuth in
heading, measured clockwise from North, [0 - 360]. [Default writes all acceptable
segments, regardless of orientation].

-Ccourse_change
Terminate a segment when a course change exceeding course_change degrees of heading
is detected [ignore course changes].

-Dminimum_distance
Do not write a segment out unless it is at least minimum_distance units long [0]

-Fxy_filter/z_filter
Filter the z values and/or the x,y values, assuming these are functions of d
coordinate. xy_filter and z_filter are filter widths in distance units. If a filter
width is zero, the filtering is not performed. The absolute value of the width is
the full width of a cosine-arch low-pass filter. If the width is positive, the data
are low-pass filtered; if negative, the data are high-pass filtered by subtracting
the low-pass value from the observed value. If z_filter is non-zero, the entire
series of input z values is filtered before any segmentation is performed, so that
the only edge effects in the filtering will happen at the beginning and end of the
complete data stream. If xy_filter is non-zero, the data is first divided into
segments and then the x,y values of each segment are filtered separately. This may
introduce edge effects at the ends of each segment, but prevents a low-pass x,y
filter from rounding off the corners of track segments. [Default = no filtering].

-Ntemplate
Write each segment to a separate output file [Default writes a multiple segment
file to stdout]. Append a format template for the individual file names; this
template must contain a C format specifier that can format an integer argument (the
running segment number across all tables); this is usually %d but could be %08d
which gives leading zeros, etc. [Default is splitxyz_segment_%d.{txt|bin},
depending on -bo]. Alternatively, give a template with two C format specifiers and
we will supply the table number and the segment number within the table to build
the file name.

-Qflags
Specify your desired output using any combination of xyzdh, in any order. Do not
space between the letters. Use lower case. The output will be ASCII (or binary, see
-bo) columns of values corresponding to xyzdh [Default is -Qxyzdh (-Qxydh if only 2
input columns)].

-S Both d and h are supplied. In this case, input contains x,y,z,d,h. [Default
expects (x,y,z) input, and d,h are computed from delta x, delta y. Use -fg to
indicate map data; then x,y are assumed to be in degrees of longitude, latitude,
distances are considered to be in kilometers, and angles are actually azimuths.
Otherwise, distances are Cartesian in same units as x,y and angles are
counter-clockwise from horizontal].

-V[level] (more ...)
Select verbosity level [c].

-bi[ncols][t] (more ...)
Select native binary input. [Default is 2, 3, or 5 input columns as set by -S].

-bo[ncols][type] (more ...)
Select native binary output. [Default is 1-5 output columns as set by -Q].

-d[i|o]nodata (more ...)
Replace input columns that equal nodata with NaN and do the reverse on output.

-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.

-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
Determine data gaps and line breaks. Do not let a segment have a gap exceeding gap;
instead, split it into two segments. [Default ignores gaps].

-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).

-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).

-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.

-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows
use just -).

-+ or just +
Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.

-? or no arguments
Print a complete usage (help) message, including the explanation of options, then
exits.

--version
Print GMT version and exit.

--show-datadir
Print full path to GMT share directory and exit.

ASCII FORMAT PRECISION

The ASCII output formats of numerical data are controlled by parameters in your gmt.conf
file. Longitude and latitude are formatted according to FORMAT_GEO_OUT, whereas other
values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
lead to loss of precision in the output, which can lead to various problems downstream. If
you find the output is not written with enough precision, consider switching to binary
output (-bo if available) or specify more decimals using the FORMAT_FLOAT_OUT setting.

DISTANCE CALCULATIONS

The type of input data is dictated by the -f option. If -fg is given then x,y are in
degrees of longitude, latitude, distances are in kilometers, and angles are azimuths.
Otherwise, distances are Cartesian in same units as x,y and angles are counter-clockwise
from horizontal.

EXAMPLES

Suppose you want to make a wiggle plot of magnetic anomalies on segments oriented
approximately east-west from a NGDC-supplied cruise called JA020015 in the region
-R300/315/12/20. You want to use a 100 km low-pass filter to smooth the tracks and a 500km
high-pass filter to detrend the magnetic anomalies. Try this:

gmt mgd77list JA020015 -R300/315/12/20 -Flon,lat,mag,dist,azim | gmt splitxyz -A90/15 -F100/-500 \
-D100 -S -V -fg | gmt pswiggle -R300/315/12/20 -Jm0.6i -Baf -B+tJA020015 -T1 \
-W0.75p -Ggray -Z200 > JA020015_wiggles.ps

MGD-77 users: For this application we recommend that you extract dist,azim from mgd77list
rather than have splitxyz compute them separately.

Suppose you have been given a binary, double-precision file containing lat, lon, gravity
values from a survey, and you want to split it into profiles named survey_###.txt (when
gap exceeds 100 km). Try this:

gmt splitxyz survey.bin -Nsurvey_%03d.txt -V -gd100k -D100 -: -fg -bi3d

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